1. Field of the Invention
This invention relates to multilayer articles having a patterned layer. The invention further relates to a method for directly depositing a patterned layer onto a substrate. The invention also relates to superconductor articles suitable for use in alternating current (ac) and time varying magnetic field applications.
2. Background of the Invention
Since the discovery of high-temperature superconducting (HTS) materials (superconducting above the liquid nitrogen temperature of 77 K) there have been efforts to develop various engineering applications using such HTS materials. In thin film superconductor devices and wires, significant progress has been made with fabrication of devices utilizing an oxide superconductor including yttrium, barium, copper and oxygen in the well-known basic composition of YBa2Cu3O7-x (hereinafter referred to as “YBCO”). Biaxially textured superconducting metal oxides, such as YBCO, have achieved high critical current densities in a coated conductor architecture, often referred to as second generation HTS wires, or a “coated conductor.” The expression “HTS wire” indicates a HTS conductor with the attributes that make it useful for the construction of a superconducting device; its cross-sectional geometry can vary from wire-like to round.
Typically, second generation HTS wires 10 include a metal substrate 11, buffer layer(s) 12, and an active layer 13, e.g., a superconductor, as illustrated in FIG. 1. The metal substrate, such as Ni, Ag, or Ni alloys, provides flexibility for the article and can be fabricated over long lengths and large areas. Metal oxide layers, such as LaAlO3, Y2O3, CeO2, or yttria-stabilized zirconia (YSZ), make up the next layer and serve as chemical barriers between the metal substrate and the active layer. The buffer layer(s) can be more resistant to oxidation than the substrate and can reduce the diffusion of chemical species between the substrate and the superconductor layer. Moreover, the buffer layer(s) can have a coefficient of thermal expansion that is well matched with the superconductor material.
To achieve high critical current densities in the wire, the superconducting material is biaxially textured. As used herein, “biaxially textured” refers to a surface for which the crystal grains are in close alignment with a direction in the plane of the surface and a direction perpendicular to the surface. One type of biaxially textured surface is a cube textured surface, in which the crystal grains are also in close alignment with a direction perpendicular to the surface.
Typically, the buffer layer is an epitaxial layer, that is, its crystallographic orientation is directly related to the crystallographic orientation of the surface onto which the buffer layer is deposited. For example, in a multi-layer superconductor having a substrate, an epitaxial buffer layer and an epitaxial layer of superconductor material, the crystallographic orientation of the surface of the buffer layer is directly related to the crystallographic orientation of the surface of the substrate, and the crystallographic orientation of the layer of superconductor material is directly related to the crystallographic orientation of the surface of the buffer layer.
Second generation HTS wire can be incorporated into a variety of devices for many applications, including cables, motors, generators, synchronous condensers, transformers, current limiters, and magnet systems. The incorporation of second generation superconducting YBCO wires into such devices provides the opportunity to dramatically reduce the device cooling requirements, thus enabling the development of lightweight, compact, high-power sources.
Many potential applications for HTS wires involve operating the superconductor in the presence of ramped magnetic or oscillating magnetic fields, or require that the HTS wire carry alternating current. In the presence of time-varying magnetic fields or currents, there are a variety of mechanisms that give rise to energy dissipation, hereinafter referred to as “ac losses.” Although second generation HTS wire is currently suitable for many types of electric power devices, including motors and power transmission cables, the ac losses from the current HTS wires are too high for use in many applications currently under development. Currently a wide, e.g., several millimeters, tape configuration is used to reach practical electrical currents. For such superconductor widths even a moderate ac frequency and magnetic field perpendicular to the superconducting film plane can produce very large ac losses.